Hearing

How do we hear?

Hearing depends on a series of events that change sound waves in the air into electrical signals. Your auditory nerve then carries these signals to your brain through a complex series of steps.

  1. Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum.
  2. The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes.
  3. The bones in the middle ear couple the sound vibrations from the air to fluid vibrations in the cochlea of the inner ear, which is shaped like a snail and filled with fluid. An elastic partition runs from the beginning to the end of the cochlea, splitting it into an upper and lower part. This partition is called the basilar membrane because it serves as the base, or ground floor, on which key hearing structures sit.
  4. Once the vibrations cause the fluid inside the cochlea to ripple, a traveling wave forms along the basilar membrane. Hair cells—sensory cells sitting on top of the basilar membrane—ride the wave.
  5. As the hair cells move up and down, microscopic hair-like projections (known as stereocilia) that perch on top of the hair cells bump against an overlying structure and bend. Bending causes pore-like channels, which are at the tips of the stereocilia, to open up. When that happens, chemicals rush into the cells, creating an electrical signal.
  6. The auditory nerve carries this electrical signal to the brain, which turns it into a sound that we recognize and understand.

Source: NIDCD (NIH)1

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How do we hear?

Healthy hearing relies on a series of events that change sound waves in the air into electrochemical signals within the ear. The auditory nerve then carries these signals to the brain.

First, sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum.

The incoming sound waves make the eardrum vibrate, and the vibrations travel to three tiny bones in the middle ear called the malleus, incus, and stapes—the Latin names for hammer, anvil, and stirrup.

The middle-ear bones amplify the sound vibrations and send them to the cochlea, a fluid-filled structure shaped like a snail, in the inner ear. The upper and lower parts of the cochlea are separated by an elastic, “basilar” membrane that serves as the base, or ground floor, upon which key hearing structures sit.

Incoming sound vibrations cause the fluid inside the cochlea to ripple, and a traveling wave forms along the basilar membrane. Hair cells that sit on top of the membrane “ride” this wave and move up and down with it.

The bristly structures of the hair cells then bump up against an overlying membrane, which causes the bristles to tilt to one side and open pore-like channels. Certain chemicals then rush in, creating an electrical signal that is carried by the auditory nerve to the brain. The end result is a recognizable sound.

Hair cells near the base of the cochlea detect higher-pitched sounds, such as a cell phone ringing. Those nearer the middle detect lower-pitched sounds, such as a large dog barking.

Source: NIDCD (NIH)2

Introduction: Hearing

Hearing depends on a series of events that change sound waves in the air into electrical signals. Your auditory nerve then carries these signals to your brain through a complex series of steps.

  1. Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum.
  2. The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes.
  3. The bones in the middle ear couple the sound vibrations from the air to fluid vibrations in the cochlea of the inner ear, which is shaped like a snail and filled with fluid. An elastic partition runs from the beginning to the end of the cochlea, splitting it into an upper and lower part. This partition is called the basilar membrane because it serves as the base, or ground floor, on which key hearing structures sit.
  4. Once the vibrations cause the fluid inside the cochlea to ripple, a traveling wave forms along the basilar membrane. Hair cells—sensory cells sitting on top of the basilar membrane—ride the wave.
  5. As the hair cells move up and down, microscopic hair-like projections (known as stereocilia) that perch on top of the hair cells bump against an overlying structure and bend. Bending causes pore-like channels, which are at the tips of the stereocilia, to open up. When that happens, chemicals rush into the cells, creating an electrical signal.
  6. The auditory nerve carries this electrical signal to the brain, which turns it into a sound that we recognize and understand.

Source: NIDCD (NIH)3

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Hearing: The ability or act of sensing and transducing Acoustic Stimulation to the Central Nervous System. It is also called audition.4

Anatomy Articles

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References

  1. Source: NIDCD (NIH): nidcd.nih.gov/ health/ age-related-hearing-loss
  2. Source: NIDCD (NIH): nidcd.nih.gov/ health/ otosclerosis
  3. Source: NIDCD (NIH): nidcd.nih.gov/ health/ age-related-hearing-loss
  4. Source: MeSH (U.S. National Library of Medicine)

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Note: This site is for informational purposes only and is not medical advice. See your doctor or other qualified medical professional for all your medical needs.